Process of producing low carbon alloys



Patented May 6, l$30 UNITED. STATES PATENT OFFICE PROCESS OF PRODUCINGLOW CARBON ALLOYS No Drawing.

This invention relates pri irily to a method of eliminating from metalsor alloys of metals the excess of carbon which remains therein after thestep of reduction of the ore 5 by the carbon method, and has for its ob-15 metals of the chromium series, or two alloying metals, such, forinstance, as chormium and nickel. it being understood, however that theinvention is not limited in its application to these particular metals.

In the production of chromium for alloying purposes, the principalsource of which is the iron-chromium mineral known as chromite, it iscommon to reduce the oxides of iron and chromium by heating the ore inan electric furnace in the presence of an excess of carbon. But thisleaves the metallic iron and chromium with sucha high carbon contentthat it is useless for most alloying or addition purposes, for whichreason the resultant alloy must be further treated by what is usuallytermed the oreing down process, which consists in strongly heating theferro alloy and carbon with additional chromite ore and therebyoxidizing a substantial portion of the remaining carbon. F erro-alloysof chromium and the like are also produced by the socalled thermitprocess, according to which metallic silicon or aluminum is used as areducing agent. But these methods are both ob- .jectionable because ofhigh metal losses or expense of reagents employed.

The present invention provldes a method of further reducing, or reducingto an unobjection ab'le proportion, the carbon constit1ipent offerro-alloys produced by the usual earbon method of reduction, and it isbased n the discovery' th'at if the high carbon roalloyjbe melted in asilica lined electric furnace, and the bath be then heated to a termperature somewhat higher than is ordinarily Application flled May 29,1926. Serial No. 112,692.

required for ingot or casting production, for some cause, possiblycatalytic action induced by the alloying metal, the order of affinity ofoxygen, as between silicon and carbon, is reversed and a violentreaction sets up between the carbon of the alloy and the silica of thefurnace lining and slag (such reaction being represented probably by theformula 2C plus SiO- equals Si plus 2C0) and the ebullition of thecarbon monoxide gas. produces violent boiling that insures good contactbetween the furnace lining and slag and all parts of the metal bath. Bythis procedure I have found it possible to reduce carbon from aproportion of more than 1% to a proportion of about 15% in less thanthree minutes from the time the bath commences to boil; and by thismethod I am enabled to produce a superior low carbon alloy from a chargeaveraging considerably higher than the permissible proportion of carbon,with very much less expense than if the low carbon alloy be produced bythe use of alloying metals that were of low carbon content beforeaddition. For instance, if it be proposed to produce high percentagechrome-nickel steel, the present process admits of the use of a verymuch cheaper grade of ferro chrome, with respect to the proportion ofcontained carbon impuritygthan can possibly be used with the ordinarymethods of producing high percentage chrome-nickel steel, the reason forthis being that with the process of the present invention the excess ofcarbon can be eliminated from the bath after addition of the alloyingmetals, and this elimination can a be accomplished by the relativelyinexpensive expedient of using a silica lining and slag, and running upthe temperature of the bath sufiiciently beyond mere fusion to set upthe 7 (probably in accordance with the reaction .plus SiO equals 2C0plus Si), which point of temperature can readily be recognized byviolent boiling effect which will be produced by the ebullition of COgas; and continue this temperature until the reduction of the carbon iscompleted, the attainment of which will be manifest fromthedi'sappearance of the violent ebullition.

The process of the present invention can be used for the treatment ofhigh carbon iron-chromium or nickel-iron-ehromium or other ferro alloysto produce low carbon ferro alloys suitable for use in steel making. Forinstance, take ferro-chrome containing 65% of chromium, 32% of iron, and3% of carbon; charge the same into an electric furnace having a silicalining; heat the bath to the fusing point of the ferro-alloy; then raisethe temperature of the bath to about, say, 3000 F. or more; maintainthis temperature until ocular indication of the reaction (violentebullition followed by a subsidence of reaction) indicates completion ofthe reaction, or until analysis shows a carbon content of 1% and siliconcontent of 3 or such variation of the silicon content as will be causedby losses; and then draw off the bath.

The process of the present invention may also be used in the productionof heat or corrosion-resisting ingots or castings, wherein the contentof nickel, chromium, or the like is high, by charging high carbonferro-alloysinto a silica furnace and causing reduction of the carbon bythe described high temperature treatment, just prior to tapping thefurnace.

WVhile I have herein referred to the electric furnace as the preferredinstrumentality for developing heat required, the invention is notlimited to the use of such a furnace, but may be carried on in an acidor silica lined induction furnace, or even in an acid open hearthfurnace.

Metal coming from the process herein described naturally carries arelatively high silicon content, the percentage corresponding closely inmost cases to that which was necessary to satisfy the carbon in thereaction described, but if the resultant proportion of silicon beobjectionable, the alloy produced by this acid process may be reduced byoxidizing the excess of silicon with ore or air, or the alloy may betransferred to a furnace with a basic lining, and the silicon veryrapidly and completely eliminated without the re-introduction of carbon.Thus, by the double process it'becomes possible to produce alloycastings or ingots or pigs practically free from both carbon andsilicon. Moreover, the double treatment renders the alloy extremely lowin impurities such as phosphorus and sulphur. But most moltenheat-resisting and corrosion-resisting steels, of which chromium andnickel are substantial constituents, use appreciable percentages ofsilicon, hence, in many instances the material obtained by the firstprocess, in which the carbon is eliminated, will be ready for its finaluse.

An important condition of the process herein described is that it isessentially re ducing and strongly so, whereas processes heretoforeemployed for reducing the carbon content of ferro alloys are distinctlyoxidizing and involve a waste of alloying metal.

' While I have described my process as used in connection with chromiumand nickel alloys, it may, of course, be employed in lowering the carboncontent of any alloy having the proper ingredients to effect thereduction of SiO by carbon at the relatively low temperatures possiblein metal melting practice.

I claim:

1. The process of producing low carbon silicon containing ferro-alloysand incorporating the same into a mass of steel to be alloyed, whichconsists in subjecting the mass of steel together with the high carbonferroalloy to a temperature materially in excess of the fusing point ofthe bath while in the presence of silica, and thereby causing the oxygen-of the silica to combine with carbon in the bath and the silicon to beadded to the bath, and to cause ebullition throughout the mass of steel;oxygen from external sources being excluded from the bath during theprocedure.

2. The process of reducing the carbon content of a ferro alloy, whichconsists in heating the ferro alloy to its fusing point and then heatingthe ferro alloy to a materially greater degree and up to the point atwhich oxygen reverses its afiinity as between silicon and carbon; theferro alloy being in contact with silica at least at a time when it isat the last named temperature and for a period sufiicient to efiect thedesired degree of reduction in the carbon content, but beingsubstantially free from contact with other oxides during the procedure.

Signed at Chicago Heights, Illinois, this 19th day of May, 1926.

FRANK ALFRED FAHRENWALD.

